Turquoise

Specific Gravity: &nbsp;2.80
Refractive Index: &nbsp;1.61-1.65
Birefringence (DR): &nbsp;0.040
Luster: &nbsp;Waxy to dull
Crystal Structure: &nbsp;Triclinic
Composition: &nbsp;hydrated copper aluminum phosphate
Hardness: &nbsp;6

Turquoise is one of the first gemstones to be mined. It has long been prized for its intense color. That varies from sky-blue to green, depending upon the amount of iron and copper within it. Turquoise is commonly found in microcrystalline, massive form, usually as encrustations, in veins, or nodules. It is opaque to semi-translucent, light, and very fragile, with a conchoidal fracture.

A Turquoise stone can be very porous, leading to fading and cracking. So, it may be impregnated with wax or resin to maintain its appearance. The Turquoise stone is thought to warn the wearer of danger or illness by changing color. It has been imitated by stained howlite, fossil bone or tooth, glass, chalcedony, limestone, and enamel.

In 1972, an imitation turquoise was produced in France by Gilson. A laboratory-made stone has a uniform color. The most popular imitation is the one called ‘imitation turquoise.’ It displays black veins on its surface.

Turquoise is usually cut and polished en cabochon. The rough of the stone occurs as a thin crust on the matrix. It was common to engrave and inlay turquoise with gold in ancient times and use it as an ornament. The finest sky-blue turquoise has been mined in Iran for more than 3,000 years. Its distinctive color is due to the presence of copper and traces of iron. Persian turquoise made its way to Europe via Turkey. Hence, its name is derived from the word ‘Turkish.’

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Occurrence

Sky-blue turquoise from Iran is generally regarded as the most desirable. On the other hand, a green variety occurs in Tibet, China. Localities in Mexico and the USA produce a greener, more porous material that tends to fade more quickly. Other localities include the former USSR, Turkestan (China), Cornwall (England), Australia, and Chile.